Electric image formation and control apparatus



Oct. 19, 1954 A. w. HOGAN 2,692,300

ELECTRIC IMAGE FORMATION AND CONTROL APPARATUS Filed July 6, 1950 2Sheets-Sheet l y l 2 AJWQHOGAN Oct. 19, A. W. HOGAN ELECTRIC IMAGEFORMATION AND CONTROL APPARATUS Filed July 6, 1950 2 Sheets-Sheet 2 SCANBLANK VIDEO FIG.4. 5H9

"k U U L 56 A 1 M O A. W. HOGAN mum jwh Patented Oct. 19, 1954 ELECTRICIMAGE FORMATION AND CONTROL APPARATUS Alsede W. Hogan, Berwyn, Md.

Application July 6, 1950, Serial No. 172,370

3 Claims. (01. 178-6.8) (Granted under Title 35, U. S. Code (1952),

sec. 266) This invention relates to electronic image. formation andcontrol and more particularly to con-- trol circuits wherein deviceswhich are capable of forming an electron image in response to an opticalimage can be controlled to produce high speed electronic shuttereffects, thereby to utilize the instantaneous electron image so formedto produce a desired visible image either during a single or series ofcontrol periods.

The image photo-tube is well known as a device which will produce avisible image on its fluorescent screen which corresponds to the opticalimage focused on its photo-cathode when proper operating voltages areapplied to the tube electrodes. The circuit of the present inventionprovides for application of controlled duration operative voltages tothe electrodes of such a tube for the purpose of producing a visibleimage on the fluorescent screen which corresponds to the opti cal imagefocused on the photo-cathode during the application of the operativevoltages. By making the duration of the application of the sweep ratesor other convenient rates even when the control voltage is applied tothe accelerator electrode for a very short period of time because thetarget, when energized, retains the image formed thereon for aconsiderable period of time due to its persistence characteristic. Sucha device can be used as a photographic shutter to obtain exposures asshort as desired by controlling the length of time operative voltage isapplied to the accelerator electrode. This embodiment has the additionaladvantage that the camera or viewing location can be remote from theevent under observation since means for transmitting duce a stationaryimage of a rotating object by operative voltages sufficiently shortsuch, for example, as of the order of one microsecond, any motion of theobject which provides the optical image on the photo-cathode will not beapparent in the visual image that appears on the fluorescent screen.Such a device is well suited to act as a shutter for a camera, eitherfor a single exposure upon the application of operative voltages once orfor repeated exposures of the intermittent motion picture type whereinthe operative voltages for the electronic shutter are appliedsuccessively, once each frame, for example. Such a device is also Wellsuited to act as a stroboscope in which case the repetition rate ofapplication of operative voltages is controlled.

The image orthicon is well known as a device which can be used tomodulate an electric current in accordance with the intensity of lightat a given point of an optical image as an electron beam sweeps thetarget energized in accordance with the optical image. Energization ofthe target occurs only when the accelerator electrode is supplied withthe proper voltage. The present invention provides means for supplyingthis voltage for a controlled period of time thereby making theenergization of the target correspond to the optical image as it appearsduring the application of the control voltage to the acceleratorelectrode. This image information on the target can be converted into amodulated voltage or current by conventional scanning means and thenconverted to a visible image by conventional television receiver meansto complete the system of the present invention.

The scanning of the target and receiver means may be conventional'andemploy the standard adjusting the repetition rate of the voltage pulsessupplied to the accelerator electrode into synchronism with therecurring condition of the object.

It is an object of this invention to provide improved control circuitsfor electron image devices.

Another object is to provide means for controlling the transition of theelectron image of such a device.

A further object is to provide means whereby an electron image devicecan be utilized as a light shutter having an extremely wide range ofoperating speeds.

A further object is to provide means whereby an electron image devicecan be utilized as a stroboscope.

An additional object is to provide a system for accurately synchronizingan electron image device shutter with the recurring condition of theobject being photographed or observed.

Another object is to provide means for high speed photography athigh'ambient light levels.

Still another object resides in the provision of an absolutely noiselessshutter.

Other objects and many of the attendant advantages of this inventionwill be readily appreciated as the same becomes better understood byreference to the following detailed description when considered inconnection with the accompanying drawings wherein:

. Fig. 1 is a diagrammatic view showing the electronic shutter controlsystem according to the preferred embodiment of the present inventionemploying an image photo-tube and arranged to photograph a projectile inflight;

Fig. 2 is a view showing schematically the means for obtaining propervoltage distribution among the electrodes of the image photo-tube inaccordance with the principle of the preferred embodiment of theinvention;

Fig. 3 is a view of the electronic shutter control system of theinvention according to another embodiment thereof employing standardtelevision equipment including the image orthicon; and

Fig. 4 is a diagrammatic view of an additional embodiment of theinvention employing the image orthicon.

Referring now to Fig. 1 there is shown thereon an image photo-tube llused to provide a light image Ill on its fluorescent screen I2 of thepro jectile I3. Such an image can be photographically recorded byfocusing camera M on screen I 2 and enclosing the screen l2, camera I4and lens 19 in a light tight enclosure 16.

The formation of the light image can be described as follows. An opticalimage ll of the projectile I3, or other object, is focused by suitablemeans such as lens IS on the photo-cathode l8 of photo-tube II whichproduces an electron image. The electron image corresponds to theoptical image I! .and will be transmitted and focused on the fluorescentscreen 52 if the proper voltages are applied to the tube electrodes.Under these conditions the electron image impinging upon the fluorescentscreen l2 will produce a visible image it of projectile 13..

Voltage divider means designated generally as 2| supplies the correctproportion of the modulator voltage to each electrode of tube H, as willbe more fully explained hereinafter. The modulator voltage appearsacross the modulator load resistor 22 and preferably is a rectangularvoltage pulse of the type well known in radar applications. Arectangular voltage pulse is preferable because it utilizes thepermissible exposure time with maximum efliciency, i. e., the lightoutput of the fluorescent screen increases with voltage amplitude. Witha rectangular pulse the voltage amplitude is maximum for the entireduration of the pulse. Thus, a square wave pulse is particularlyessential where the exposure times are of extremely short duration.Also, if the photo-tube is not shielded from stray magnetic fields theelectron image will move across the fluorescent screen if the pulsevoltage is allowed to vary, i. e., depart from a rectangular shape. Suchmovement would result in a poor quality of output image. By making thelight tight enclosure 6 of such material that it will shield thephoto-tube II from external magnetic fields, the applied voltage pulsemay depart from rectangular shapes without resulting in movement of theimage on the fluorescent screen I2 during the pulse.

The rectangular voltage pulse is derived in synchronism with the eventto be recorded by any convenient system such as that shown in Fig. 1,for example. In the system of Fig. 1, a continuous light source isprovided and a contacting device comprising contact elements 23 and 24is located in the field of view of the optical system I9 in a mannersuch that electrical contact occurs between the elements 23 and 24 ofthe contacting device when the projectile Hi from gun is also in thefield of View. When this contact occurs, a positive voltage from battery25 appears on grid 28 of thyratron 2'! by means of capacitor 28. Tube2'! is thereby made conductive and discharges the artificialtransmission line 29 through resistor 3 I, producing a rectangularvoltage pulse at the input terminals 32 of modulator 33. The modulatoramplifies this pulse to the proper amplitude and preserves itssubstantially rectangular shape across load reinstant when theprojectile I3 is in the field of the optical system and produces animage only for the duration of the voltage pulse.

In photographing high speed phenomena, it is essential that theeffective exposure time be sufiiciently short so that any motion of theobject being photographed will produce negligible motion of the imageproduced on the film by the lens and shutter system. The system of Fig.1 is well suited for achieving short effective exposure times since theeffective exposure time will be the same as the duration of the voltagepulse supplied by modulator 33. Pulse widths as short as one microsecondand less are now commonplace with such equipment.

When short duration pulses of this type are applied to a voltage dividersuch as that formed by resistors R1, R2, R3, and R4, it will be foundthat the proportion of the voltage across each resistor will not be thesame as it would be if a D. C. voltage were applied. This is becauseshort pulses behave in a manner similar to high frequency A. C. voltagesin that the capacity in shunt with the resistors R1 to R4 controls thevoltage division when the capacitive reactances are smaller in magnitudethan the respective resistances. To obtain the correct voltage divisionamong the tube electrodes regardless of pulse width the presentinvention provides the proper capacitance ratio between these electrodesas well as the proper resistance ratio.

Referring now to Fig. 2, the manner in which this voltage division isachieved will be more fully described. The image photo-tube II has aphoto-cathode i3 and four concentric cylindrical electrodes 4|, '42, Q3and 44. The distributed capacitances between adjacent pairs of theseelectrodes are represented by dashed line capacitors C11, C12, C13 andC14. The resistor values for the divider 2| are calulated by means ofOhms law for direct current. The capacitor values for such a divider arecalculated by means of Ohms law for alternating current. For example,suppose the modulator output pulse has an amplitude of 4000 volts forpulses of all Widths. Also, assume that the desired voltages at pointsalong the divider with respect to the photo-cathode 18 are E1=15,E2=100, E3=600 and E4=4000 volts. The total value of resistance Rtshould be as low as practical in order to have low RC constants whichare necessary to maintain a good wave shape for the modulator pulse.

Assume a total resistance, Rt, of one megohm and negligible currentflowing into the image photo tube. Then according to Ohmslaw for directcurrent:

and the same current flows through all resistors R1 to R4.

and,

All.

In order to have a minimum number of condensers in the divider and alsoto eliminate the necessity of procuring a condenser with a 3400 voltrating the present invention eliminates an external condenser across R4and relates the other condensers to the capacitance Cn.

To illustrate this, assume that and, generally XC=KE The voltages and 04have been predetermined, therefore,

C =1O muf. (given) Values of the external condensers are then,

By choosing the values of resistors R1 to R4 and capacitors C91 to Ce3in the manner herein set forth, proper voltage division will be obtainedfor all pulse widths supplied by the modulator.

Referring now to Fig. 3, a second embodiment of the present invention isshown wherein an image orthicon television pick-up tube 54 is utilizedas a light shutter in a stroboscope. Obviously the same arrangementcould be used as a camera shutter by focusing a camera on the kinescopescreen 55 and enclosing the camera and screen 55 in a light tightenclosure. Single pulse or repetitive pulse means in place ofmultivibrator 55 are also obvious modifications to those skilled in theart. Rated voltages for the tube are applied to the tube electrodes suchas 19, for example, except as set forth hereinafter. The voltage onelectrodes 51 and 58 is the rated value only during the time ofapplication of the operative pulse in accordance with the teaching ofthis invention...

A continuous light source 20 illuminates the object under observationsuch as the rotating propeller 60. An optical system [9 focuses theimage of propeller 60 on the photo-cathode 51 forming an electron imagewhich energizes the target 58 when the proper voltage exists on theintervening accelerator 59. Conventional scanning circuits 6| operatecontinuously and convert the target image, when present, into amodulated video signal which is applied to kinescope 62 or othersuitable cathode-ray tube by video circuit 83 after mixing with theusual blanking signals from blanking circuit 64. The deflection orscanning circuits 6| for the kinescope 62 and the image orthicon 54 aresynchronized so that the kinescope 62 reproduces on its screen 55 animage corresponding to that on the target 58. This operation is that ofthe conventional television system where the link between the imageorthicon circuit and the kinescope circuit may be made by means ofcables as shown in Fig. 3 or by a radio link as is well known in theart.

The circuit of the present invention provides means for controlling theapplication of operative voltage to accelerator 59 so that theenergization of the target 58 corresponds to the image focused on thephoto-cathode 51 only during the application of operative voltage. Theeffective exposure time, therefore, is equal to the time duration of theoperative voltage pulse. When accelerator 59 does not have operativevoltage applied thereto, no image signal reaches the target 58. Bysynchronizing the repetition frequency of the pulses from multivibrator56 integrally with the speed of revolution of propeller 60 a stationaryimage will be obtained on the screen 55. Here again, to be satisfactory,the pulse duration must be sufiiciently short to prevent any motion ofthe propeller during the pulse from producing any apparent motion in theimage produced on screen 55. This criterion is related to the overallresolution of the system. It may further be desired to maintain thepulse repetition frequency of multivibrator 56 lower than the rate ofscanning the target 58 to prevent the incidence upon target 58 of morethan one electron image each time the target is scanned.

Operative voltage pulses may be supplied by any convenient means such asthe multivibrator 56 with its output voltage, of polarity as shown,applied to a suitable voltage divider 65 comprising resistors R5, R6 andR7. The voltage divider is so arranged that the relative magnitudes ofthe voltages applied to the electrodes 51, 58 and 59 are the ratedoperating voltages for the particular tube 54 during the time ofapplication of the operative pulse. The design of such a voltage dividerincluding added capacitors Cei, Ce5 and Cee to obtain the propercapacitance ratio can be carried out in a manner similar to that setforth in detail in relation to Fig. 2. The duration of the pulse can beas short as desired because the image produced thereby on the target 58will persist for a sufiiciently long period for a complete scan of thetarget to occur. The image, therefore, will have characteristics of anextremely rapid exposure corresponding to the short pulse applied andcan be converted into the video signal by completing the scan of thepersistent image between pulses.

Referring now to Fig. 4 there is shown a further embodiment of theinvention as a modification of the system of Fig. 3 which may be used toadvantage in some situations. In this circuit the grid controlleddischarge tube 61 is utilized to cut off the electron beam in tube 54except during pulses from multivibrator 56. Obviously, in this case, theonly voltage pulses that can be used are those having a duration notless than the time required for one complete scan of the target 58. Thisis so because at the end of the voltage pulse from multivibrator 55 theelectron beam scanning target 58 is cut off until the start of the nextpulse, thus making video signals available only during the applied pulseperiod.

The circuit of Fig. 4 accomplishes beam blanking by applying a portionof the applied pulse from potentiometer 10 through coupling capacitor 68to the grid 69 of tube 61. Tube 61 is biased by bias means H andpotentiometer 72 to be normally conductive, thereby maintaining itsplate 73 negative with respect to ground by an amount sumcient to blankthe scanning beam of tube 54. This control is obtained by connectinggrid 14 of the image orthicon 54 to plate 13 of tube 57 by means of lead75. Plate E3 is normally negative because the B supply 16 has itspositive terminal grounded at 11 and the current in tube 61 produces avoltage drop in resistor 78. During the negative voltage pulse frommultivibrator 55, tube 61 becomes less conductive thereby reducing thevoltage drop in resistor 18. The potential of plate 13 and hence grid 74of tube 54 is thereby raised to a value which permits normal beamcurrent in tube 54.

The modification shown in Fig. 4 can be used whenever the desiredexposure time is equal to or greater than the time required for acomplete target scan with the deflection circuits employed. By blankingthe beam in the manner set forth a lower noise level results in thevideo circuit which in turn afiords a more distinct image at thereceiving cathode-ray tube 62.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

The invention described herein may be manufactured and used by or forthe Government of the United States of America for governmental purposeswithout the payment of any royalties thereon or therefor.

What is claimed as new and desired to be secured by Letters Patent ofthe United States is:

1. In a system for observing high speed phenomenon, a light sensitiveelectrode for producing an electron image corresponding to theinstantaneous view of said phenomenon, means for producing a voltagepulse of short duration, an electron responsive target for producing adetectable image corresponding to said electron image when the latter isprojected on said target, accelerator electrodes for electron opticallyfocusing said electron image on said target, and voltage divider meansincluding parallel capacitive and resistive branches connected betweenadjacent electrodes for applying said pulse to said acceleratorelectrodes, means for applying said pulse across said voltage dividermeans, said resistive branches producing a predetermined direct-currentvoltage distribution between adjacent electrodes, said capacitivebranches having values such that the total capacitance between adjacentelectrodes produces an alternating-current voltage distributiontherebetween corresponding to said predetermined direct-current voltagedistribution.

2. In a system for observing high speed phenomena, means for producing asingle non-recurring voltage pulse of short duration, an image phototubeincluding a light sensitive electrode for producing an electrode imageat said light sensitive electrode corresponding to the instancous viewof an optical image projected thereon, a screen in" said tube having apersistence longer than the duration of said pulse and a plurality ofaccelerated electrodes in said tube between said light sensitiveelectrode and said screen, potential divider means connected to saidpulse producing means and to each of said electrodes for applying saidpulse to said electrodes to thereby accelerate said electron image andproject the electron image on said screen, said screen producing avisible image of relatively longer duration than said pulse uponapplication of said electron image thereto, and said potential dividermeans comprising a plurality of parallel capacitive and resistivebranches connected between adjacent electrodes, said resistive branchesproducing a predetermined direct-current voltage distribution betweenadjacent electrodes, said capacitive branches having values such thatthe total capacitance between adjacent electrodes produces analternating-current voltage distribution therebetween corresponding tosaid predetermined. direct-current voltage distribution.

3. In an apparatus for observing high speed phenomena including a tube,a light sensitive electrode in said tube for producing an electron imagecorresponding to the instantaneous View of an optical image projectedthereon, means for producing a voltage pulse of short duration, anelectron responsive target in said tube for producing a detectable imagecorresponding to said electron image when the latter is projected onsaid target, accelerator electrodes in said tube between said lightsensitive electrode and said target, voltage divider means electricallyconnected to said pulse producing means and including parallel resistiveand capacitive branches connected between the adjacent electrodes forapplying said pulse to said accelerator electrodes to therebyelectron-optically focus said electron image on said target, saidresistive branches producing a predetermined direct-current voltagedistribution between adjacent electrodes, said capacitive brancheshaving values such that the product of the total capacitance betweeneach of the adjacent electrodes and the direct-current voltagetherebetween equals the product of the interelectrode capacitancebetween the pair of accelerator electrodes nearest said target and thedirect-current voltage between said last named electrodes.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,189,319 Morton Feb. 6, 1940 2,198,479 Langmuir Apr. 23, 19402,234,806 Ploke Mar. 11, 1941 2,251,786 Epstein Aug. 5, 1941 2,256,523Lubszynski Sept. 23, 1941 2,287,298 Dillenburger June 23, 1942 2,373,114Goldsmith Apr. 10, 1945 2,382,981 Eidgerton Aug. 31, 1945 2,402,053 KellJune 11, 1946 2,421,182 Bayne May 27, 1947 2,505,060 Oliver Apr. 25,1950

